The information that you have provided does not match anything that I have seen ( which is not a lot) and seems to be different then this web site https://www.mg-cars.org.uk/news/news498.html lists too. Maybe you can give us more information on the car model, year, and description of the engine. Does it have a flat head or a overhead valve engine? If the latter, then look on the side of the block toward the front and look for a casting number, 900, 950, 1100, these are going to be the overhead valve engines listed on this web site.
Let us know where you got this number from, on the car or the registration documents? All of these things will help you and us narrow down what you have.